U.S. patent number 6,268,404 [Application Number 09/370,710] was granted by the patent office on 2001-07-31 for radiation-curable organosiloxane coating compositions.
This patent grant is currently assigned to Th. Goldschmidt AG. Invention is credited to Hardi Dohler, Thomas Ebbrecht, Winfried Hamann, Peter Lersch, Stefan Stadtmuller.
United States Patent |
6,268,404 |
Dohler , et al. |
July 31, 2001 |
Radiation-curable organosiloxane coating compositions
Abstract
This invention provides radiation-curing coating compositions
comprising a mixture of organopolysiloxanes modified laterally and
terminally with acrylic groups, which exhibit markedly improved
adhesion to a variety of substrates following curing and for which
there is little or no change in the adhesiveness on storage for
prolonged periods.
Inventors: |
Dohler; Hardi (Hattingen,
DE), Ebbrecht; Thomas (Bochum, DE), Hamann;
Winfried (Essen, DE), Lersch; Peter (Oberhausen,
DE), Stadtmuller; Stefan (Essen, DE) |
Assignee: |
Th. Goldschmidt AG (Essen,
DE)
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Family
ID: |
7877112 |
Appl.
No.: |
09/370,710 |
Filed: |
August 9, 1999 |
Foreign Application Priority Data
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Aug 11, 1998 [DE] |
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198 36 246 |
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Current U.S.
Class: |
522/99; 427/515;
427/516; 428/352; 428/447; 522/172; 525/474; 525/477; 525/479;
528/33 |
Current CPC
Class: |
C09D
183/06 (20130101); C09D 183/06 (20130101); C08L
83/00 (20130101); Y10T 428/31663 (20150401); Y10T
428/2839 (20150115) |
Current International
Class: |
C09D
183/06 (20060101); C09D 183/07 (); C08F 002/46 ();
C08L 083/07 () |
Field of
Search: |
;522/99,172
;528/26,32,33,41 ;525/477,479,474 ;428/352,447 ;427/515,516 |
References Cited
[Referenced By]
U.S. Patent Documents
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4908274 |
March 1990 |
Jachmann et al. |
4963438 |
October 1990 |
Weitemeyer et al. |
4978726 |
December 1990 |
Dohler et al. |
5034491 |
July 1991 |
Wewers et al. |
5552506 |
September 1996 |
Ebbrecht et al. |
5977282 |
November 1999 |
Ebbrecht et al. |
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Foreign Patent Documents
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27 47 233 C3 |
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Jul 1978 |
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DE |
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29 48 708 C2 |
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Aug 1980 |
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DE |
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38 20 294 C1 |
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Oct 1989 |
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DE |
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38 10 140 C1 |
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Oct 1989 |
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DE |
|
Primary Examiner: Berman; Susan W.
Attorney, Agent or Firm: Frommer Lawrence & Haug LLP
Claims
What is claimed is:
1. A radiation-curing coating composition comprising
(A) from about 10 to about 90% by weight, based on the total weight
of (A) and (B), of one or more laterally modified
organopolysiloxanes of the general formula (I) ##STR13##
(B) from about 10 to about 90% by weight, based upon the total
weight of (A) and (B), of one or more terminally modified
organopolysiloxanes of the general formula (II) ##STR14##
in which R.sup.1 and R.sup.2 are as defined above and
c=5 to 500.
2. A radiation-curing coating composition as claimed in claim 1,
wherein R.sup.1 is methyl.
3. A radiation-curing coating composition as claimed in claim 1,
wherein a is from 0 to 200.
4. A radiation-curing coating composition as claimed in claim 1,
wherein b is from 3 to 20.
5. A radiation-curing coating composition as claimed in claim 1,
wherein c is from 5 to 300.
6. A radiation-curing coating composition as claimed in claim 1,
wherein the components of structures (I) and (II) are present in a
ratio of from about 80% by weight:about 20% by weight to about 20%
by weight:about 80% by weight.
7. A radiation-curing coating composition as claimed in claim 1,
wherein the components (I) and (II) are present in a ratio of from
75% by weight:25% by weight to 25% by weight:75% by weight, and a=0
to 100, b=5 to 15 and C=15 to 200.
8. A radiation-curing coating composition as claimed in claim 1,
which comprises 10 to 90% by weight of formula (I) and 10 to 90% by
weight of formula (II) and wherein
R.sup.1 =identical or different aliphatic or aromatic hydrocarbon
radicals of 1 to 10 carbon atoms,
R.sup.2 =a linear, branched or aromatic hydrocarbon radical of 1 to
20 carbon atoms, with or without ether bridges, to which there are
attached, by way of ester linkages, from 1 to 5 acrylic and/or
methacrylic acid units and, optionally, monocarboxylic acid units
of 2 to 10 carbon atoms which are free of polymerizable double
bonds,
R.sup.3 =R.sup.1 or R.sup.2,
a=0 to 300,
b=1 to 25, and
c=5 to 50.
9. A radiation-curing coating composition as claimed in claim 1,
wherein R.sup.2 is ##STR15##
10. A radiation-curing coating composition as claimed in claim 1,
wherein the laterally modified organosiloxane is a mixture
comprising two organosiloxanes of formula (I) where ##STR16##
a is 15 and b is 5; and ##STR17##
R.sup.3 is CH.sub.3, a is 10, and b is 4; and
the terminally organo-modified organopolysiloxane is a mixture
comprising two organosiloxanes of formula (II) when ##STR18##
R.sup.3 is CH.sub.3, and c is 80.
11. An adhesive release coating which comprises a radiation-curing
coating composition according to claim 1.
12. An adhesive release coating according to claim 11, which
further comprises curing initiators, fillers, pigments,
organopolysiloxane(meth)acrylates, acrylate systems or
additives.
13. A method for coating a material which comprises applying a
radiation curing composition according to claim 11, to the surface
of said material.
14. The method according to claim 13, where the material is
plastic, paper, wood, or metal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radiation-curable coating
compositions having improved properties, such as adhesion to the
substrate and release properties which are stable over time.
2. Background of the Invention
Polysiloxanes containing acrylate acid ester groups (acrylate
groups) have become established as binders which can be cured under
high-energy radiation for applications such as printing inks and
for producing film-forming binders or for coating materials for
surfaces of plastic, paper, wood and metal. Curing takes place in
particular by UV radiation (following the addition of known
photoinitiators, such as benzophenone and its derivatives, for
example) or by means of electron beams.
3. Description of the Related Art
Acrylate-modified organosiloxanes are described in numerous patent
documents. The following patents and applications are cited as
representatives of the prior art.
Organopolysiloxanes in which the acrylate-containing organic groups
are connected to the polysiloxane framework by way of an Si--O--C
bond can be prepared in accordance with a process of DE-C-27 47 233
by reacting --COH-containing (meth)acrylic esters with
organopolysiloxanes which have SiX groups (X=alkoxy, hydroxyl or
chlorine) wherein the organopolysiloxanes used are of the formula
##STR1##
and the siloxane molecule has 3 to 100 silicon atoms and, as the
(meth)acrylic ester, using pentaerythritol tri(meth)acrylate, from
0.05 mol to equimolar amounts of the pentaerythritol ester being
employed relative to COH and SiX groups.
In a modification of this process the procedure in accordance with
DE-C-29 48 708 is to react organopolysiloxanes of the formula
##STR2##
(R.sup.1 =alkyl of 1 to 4 carbon atoms, vinyl and/or phenyl with
the proviso that at least 90 mol % of the groups R.sup.1 are
methyl; a=from 1.8 to 2.2; b=from 0.004 to 0.5) first of all with
at least twice the molar amount, based on SiCl groups, of a
dialkylamine whose alkyl groups each have 3 to 5 carbon atoms and
in which the carbon atoms adjacent to the nitrogen each carry not
more than one hydrogen atom and then reacting the product of this
first reaction with at least equimolar amounts of pentaerythritol
triacrylate or pentaerythritol trimethacrylate and, subsequently,
in a manner known per se, separating off the product of the process
from solid constituents suspended in it.
Organopolysiloxanes, in which the acrylic ester-containing organic
groups are connected to the polysiloxane framework by way of Si--C
bonds can be prepared, for example, by subjecting allyl glycidyl
ether or another suitable epoxide having an olefinic double bond to
an addition reaction with a hydrosiloxane and, following the
addition reaction, esterifying the epoxide with acrylic acid to
open the epoxide ring. This procedure is described in DE-C-38 20
294.
A further possibility for the preparation of acrylate-modified
polysiloxanes with Si--C linkage of the modifying group(s) is to
subject an alcohol having an olefinic double bond, such as allyl
alcohol, to an addition reaction with a hydrosiloxane in the
presence of a platinum catalyst and then to react the OH group of
this alcohol with acrylic acid or with a mixture of acrylic acid
and other, saturated or unsaturated acids. This procedure is
described, for example, in DE-C-38 10 140.
When considering unbranched organopolysiloxanes, modification can
take place at the two terminal siloxydimethyl units or at one or
more siloxymethyl units within the siloxane chain. Accordingly, one
talks of terminally or laterally modified polysiloxanes. The
modification can also be both terminal and lateral; in the text
below, such modifications are included among the laterally modified
products.
It has been found in practice that abhesive coatings produced with
terminally (meth)acrylate-modified organopolysiloxanes on sheetlike
supports, for use in adhesive tapes or label laminates, for
example, feature low release values, which are stable over time,
since such polysiloxanes have a high silicone character which is
not interrupted by organic modifications within the siloxane chain.
To achieve good adhesion to the substrate, however, a relatively
high modification density with reactive groups is necessary. This
is difficult to achieve with terminally modified siloxanes, since
the siloxane chain would have to be shortened correspondingly. Such
short-chain terminally modified polysiloxanes are comparatively
expensive, so their use would be uneconomic.
Laterally modified silicone (meth)acrylates, on the other hand, can
be varied over wide ranges in their modification density
independently of the molecular weight. Since lateral (meth)acrylate
groups are known to be less reactive owing to their steric
hindrance, there is a risk that not all groups will react
completely during the polymerization. Such residual, uncrosslinked
acrylate groups can then enter into follow-on reactions--for
example, with the pressure-sensitive adhesive of a label
laminate--which would, over time, lead to an increase in the
release values.
OBJECT OF THE INVENTION
It is an object of the present invention to develop
radiation-curable coating compositions which have good adhesion to
the substrate and which possess release properties which are stable
over time.
SUMMARY OF THE INVENTION
It has been found that radiation-curing coating compositions
consisting of mixtures of laterally and terminally
(meth)acrylate-modified organopolysiloxanes of the general formulae
(I) and (II), described infra, possess such required
properties.
Surprisingly, it has been discovered that within such mixtures of
the invention the advantages of the individual components are
manifested whereas the disadvantages described above are
compensated by the other component and do not become effective.
While not wishing to be bound by theory, this profile of properties
could be explained by the following hypothesis. Directly after
coating on a sheetlike support, there is a gradual separation of
the mixture even before the crosslinking of the reactive units,
with the more strongly polar, laterally modified component
orienting itself toward the substrate and the less polar,
terminally modified component orienting itself toward the surface.
After curing, the laterally modified component is responsible for
good anchorage to the substrate while the terminally modified
component at the surface determines the favorable release
properties. The consequence of this for the coating compositions of
the invention is the following improved profile of properties:
1. The coating compositions of the invention, after curing, exhibit
considerably improved adhesion to a variety of substrates (such as
paper, and polymer film, for example).
2. There is little or no change in the abhesiveness of the cured
coatings on storage for prolonged periods, which would be evident
through an increase in the release values.
3. In addition, the coating compositions can be cured at high
processing speeds on support materials.
The radiation-curable coating compositions of the invention
comprising
(A) from about 10 to about 90% by weight of one or more laterally
modified organopolysiloxanes of the general formula (I)
##STR3##
(B) from about 10 to about 90% by weight of one or more terminally
modified organopolysiloxanes of the general formula (II)
##STR4##
in which R.sup.1 and R.sup.2 are as defined above and
c=5to 500.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a preferred embodiment R.sup.1 is an aliphatic or aromatic
hydrocarbon radical of 1 to 10 carbon atoms and R.sup.2 is a
linear, cyclic, aromatic or branched hydrocarbon radical of 1 to 20
carbon atoms; preferably the monocarboxylic acid unit have 2 to 10
carbon atoms.
Preference is given to mixtures of components (I) and (II) in a
ratio of from about 80:20 to about 20:80 where a=0 to 200, b=3 to
20 and c=5 to 300. Particular preference is given to mixtures of
components (I) and (II) in a ratio of from about 75:25 to about
25:75 with a=0 to 100, b=5 to 15 and c=15 to 200.
Particularly preferred groups for R.sup.2 is as follows:
##STR5##
The radiation-curing coating compositions of the invention can be
compounded with conventional curing initiators, fillers, pigments,
other acrylate systems, known per se in the art, and further
customary additives. The compositions of the invention can be
crosslinked three-dimensionally by free radicals and cure thermally
with the addition of, for example, peroxides or cure under the
influence of high-energy radiation, such as UV radiation or
electron beams, within a very short time to form mechanically and
chemically resistant films which, given an appropriate composition
of the coating compositions of the invention, have predeterminable
abhesive properties. If UV light is used as the source of
radiation, crosslinking takes place preferably in the presence of
photoinitiators and/or photosensitizers, such as benzophenone and
its derivatives or benzoin and corresponding substituted benzoin
derivatives.
Photoinitiators and/or photosensitizers are used in the coating
compositions of the invention preferably in amounts of from about
0.01 to about 10% by weight, in particular from about 0.1 to about
5% by weight, based in each case on the weight of the
acrylate-functional organopolysiloxanes.
The individual components of the coating compositions of the
invention of the general formulae (I) and (II) are compounds known
from the prior art whose preparation is described, for example, in
"Chemie und Technologie der Silicone" by W. Noll, Verlag Chemie
1968 and, for example, in the following documents and the
literature cited therein: DE-C-38 20 294, DE-C-38 10 140, U.S.
5,552,506, German Patent Application 198 08 786.1, all herein
incorporated by reference.
EXAMPLES
The examples which follow are intended to illustrate the invention,
and do not constitute any restriction whatsoever.
Terminally Modified Silicone Acrylates
##STR6## Compound R.sup.1 R.sup.2 c V1 CH.sub.3 ##STR7## 30 V2
CH.sub.3 ##STR8## 80
Laterally Modified Silicone Acrylates
##STR9## Compound R.sup.1 R.sup.2 R.sup.3 a b V3 CH.sub.3 ##STR10##
##STR11## 15 5 V4 CH.sub.3 ##STR12## CH.sub.3 10 4
Performance Testing
To test the performance properties of the coating compositions to
be used in accordance with the invention, the products of the
examples and of the comparative examples, which are not in
accordance with the invention, were applied to sheetlike supports
(oriented polypropylene film) and, following the addition of 2%
photoinitiator (Darocur.RTM. 1173, Ciba Geigy), cured by exposure
to UV light at 120 W/cm under a nitrogen atmosphere and with a belt
speed of 20 m/min. The amount applied in each case was about 1
g/m.sup.2.
Release Value
The release values were determined using various adhesive tapes
from Beiersdorf which were 25 mm wide: specifically, an adhesive
tape coated with acrylate adhesive, obtained commercially under the
designation TESA.RTM. 7475, and adhesive tapes coated with rubber
adhesive, obtained commercially under the designations TESA.RTM.
4154 and TESA.RTM. 7476.
To measure the abhesiveness, these adhesive tapes were rolled onto
the substrate and then stored at 40.degree. C. under a weight of 70
g/cm.sup.2. After 24 hours, a measurement was made of the force
required to peel the respective adhesive tape from the substrate at
a rate of 30 cm/min and a peel angle of 180.degree.. This force was
designated the release force or release value. The general test
procedure corresponds essentially to FINAT Test Method No. 10. To
test the aging behavior, the storage time was extended to 7 and 14
days under the conditions described above.
Loop Test
The purpose of the loop test is to determine rapidly the degree of
curing of a release coating. For this purpose a strip about 20 cm
long of the adhesive tape TESA.RTM. 4154 from Beiersdorf was rolled
three times onto the substrate and peeled off again immediately by
hand. Then a loop was formed by placing the ends of the adhesive
tape together, so that the adhesive faces of both ends was in
contact over an extent of about one centimeters. The ends were then
parted again by hand, during which the contact area should move
uniformly to the center of the adhesive tape. In the case of
contamination with poorly cured release material, the bond strength
of the adhesive tape was no longer sufficient to maintain the
contact area when the ends are pulled apart. In this case, the test
was said to have been failed.
Subsequent Adhesion
The subsequent adhesion was determined largely in accordance with
FINAT Test Method No. 11. For this purpose the adhesive tape
TESA.RTM. 7475 from Beiersdorf was rolled onto the substrate and
then stored at 40.degree. C. under a weight of 70 g/cm.sup.2. After
24 hours, the adhesive tape was separated from the release
substrate and rolled onto a defined substrate (steel plate, glass
plate, and film). After one minute a measurement was made of the
force required to peel the adhesive tape from the substrate at a
rate of 30 cm/min and a peel angle of 180.degree.. The value thus
measured was divided by the value given by an untreated adhesive
tape under otherwise identical test conditions. The result is
termed the subsequent adhesion and is generally indicated as a
percentage.
Rub-off Test
The adhesion of the cured coating compositions to the substrate was
determined by vigorous rubbing with the thumb. If adhesion was
inadequate, rubberlike crumbs are formed. This test is generally
referred to as the rub-off test.
TABLE 1 Blends of coating compositions consisting of components (I)
and (II) Examples according to the invention percentages by
weight): Example V1 V2 V3 V4` A 70 30 B 60 40 C 40 60 D 50 50
TABLE 2 Non-blended coating compositions (examples not in
accordance with the invention) Example V1 V2 V3 V4` E 100 F 100 G
100 H 100
TABLE 2 Non-blended coating compositions (examples not in
accordance with the invention) Example V1 V2 V3 V4` E 100 F 100 G
100 H 100
TABLE 4 Release value aging with TESA .RTM. 7475 in cN/2.5 cm after
Example 1 day 7 days 14 days A 0.2 0.2 0.3 B 0.2 0.2 0.2 C 0.1 0.1
0.1 D 0.1 0.1 0.1 E 0.2 0.2 0.2 F 0.1 0.1 0.1 G 3.1 5.9 8.7 H 2.8
5.5 8.4
The results of the performance tests of the examples in accordance
with the invention (Table 1) in comparison to the examples not in
accordance with the invention (Table 2) are set out in Table 3
(rub-off test, subsequent adhesion, release values) and Table 4
(aging behavior).
Table 3 shows that coating compositions consisting of blends of
linear siloxane acrylates (components of structure (II), V1 and V2)
and lateral siloxane acrylates (components of structure (I), V3 and
V4) feature low release values and high subsequent adhesion and at
the same time exhibit high substrate adhesion. With Examples E and
F as well, low release values and high subsequent adhesion are
found, although here the rub-off test is failed. Examples G and H
show good adhesion to the substrate with a release value which is
already high initially and which, furthermore, rises after just a
short time and points toward relatively rapid aging (Table 4).
In Table 4, on the other hand, there is no increase in the release
values for the blends A to D, which corresponds to very good aging
behavior.
The above description of the invention is intended to be
illustrative and not limiting. Various changes or modifications in
the embodiments described herein may occur to those skilled in the
art. These changes can be made without departing from the scope or
a spirit of the invention.
* * * * *